NEW YORK -- A wildlife conservation group said it is trying to pressure U.S. states to regulate carbon dioxide emissions under federal clean water laws because of harm the gas does to the cycle of life in the ocean.

Unlike most other developed countries, the United States, the world's top greenhouse gas emitter, does not regulate carbon dioxide and other gases that scientists link to global warming. Efforts by states and environmental groups to regulate CO2 through clean air laws have so far failed.

The Center for Biological Diversity, a national environmental group, on Wednesday petitioned California to regulate CO2 under the Clean Water Act. Miyoko Sakashita, an attorney for the group in San Francisco, said it would soon petition Oregon and Washington state as well as states on the East Coast to do the same.

Oceans absorb a third of the CO2 in the atmosphere and sink it to the depths. But when they absorb too much of the gas the process makes oceans more acidic. The problem is worsening as the burning of coal, oil, natural gas, and forests increase levels of the gas in the atmosphere.

Acidification can harm animals from corals to crabs, impairing their use of calcium to make shells and skeletons. It can also hurt microscopic life.

"Many species of phytoplankton and zooplankton, which form the basis of the marine food web, are also particularly vulnerable to ocean acidification," said Sakashita.

The CBD says clean water laws regulate pH levels in water and should therefore regulate CO2 emissions in oceans. While the laws are federal, states implement them.

Efforts to force the federal government to regulate CO2 emissions under clean air laws have been fruitless so far because the U.S. Environmental Protection Agency maintains that greenhouse gas does not fit the Clean Air Act's definition as a pollutant.

California water quality officials did not immediately return calls about the CBD effort.